For some reason, writing to the wake fd from the same thread in
deferred_invoke was causing a deadlock. However, we don't actually need
to wake from the same thread, since the event loop is not waiting and
will therefore process the deferred_invoke on the next iteration.
This issue was introduced in 3742138cc3.
The deadlock could be reproduced consistently by increasing
LOCAL_STORAGE_QUOTA in StorageJar.cpp to a large value like 50 MiB.
Once an event loop manager is installed, we want to be sure we only use
that manager in the current process going forward. Mixing event loop
implementations can only cause problems.
More to the point, this ensures that we have installed the AppKit or Qt
event loop managers before the first time EventLoopManager::the() is
invoked. Now that we defer this installation until we know whether we
are running headlessly, we want to be extra sure that we have done so
before any services using the event loop have started.
